The present invention relates to therapeutic medical devices and methods, and more particularly to devices and methods for improving venous blood flow in a patient.
Deep vein thrombosis (DVT) and pulmonary embolism (PE) constitute major health problems in the United States. It has been estimated that 300,000 to 600,000 hospitalizations a year are attributable to DVT and PE conditions. Venous thromboembolism is also a significant risk in surgical patient populations where preoperative, operative and postoperative immobilization with concomitant loss of venous pump function causes blood stasis.
The use of prophylactic antithrombotic drugs for preventing DVT are known to the art. However, the efficacy of prophylactic administration of anticoagulants and antiplatelet agents has been disputed, and is certainly not absolute. An alternative approach, attractive because of its freedom from hemorrhagic side effects, is the use of physical techniques such as elastic stockings, passive leg exercise, electrical calf stimulation and external pneumatic compression of the legs. Pneumatic compression has been the most studied and appears to be an effective therapeutic technique. For example, the results of a comparison trial between sequential compression and uniform compression are disclosed in article by E. W. Salzman, et al., entitled Effect of Optimization of Hemodynamics on Fibrinolytic Activity and Antithrombotic Efficacy of External Pneumatic Calf Compression, Annals of Surgery, Vol. 206, No. 5, November (1987), pp. 636-641. Salzman et al. also discloses the lack of commercially available systems for applying external pneumatic compression in an optimized manner, based on blood flow velocity and volumetric flow rate, etc. Antithrombotic modalities based on sequential pneumatic compression are also disclosed in articles by J. A. Caprini, et al., entitled Role of Compression Modalities in a Prophylactic Program for Deep Vein Thrombosis, Seminars in Thrombosis and Hemostasis, Vol. 14, Supp., Thieme Medical Publishers, Inc., pp. 77-87, (1988); and Hull, et al., entitled Effectiveness of Intermittent Pneumatic Leg Compression for Preventing Deep Vein Thrombosis After Total Hip Replacement, Journal of the American Medical Association, Vol 263, No. 17, May, 2, 1990, pp. 2313-2317. Devices for performing sequential compression have also been patented. For example, U.S. Pat. No. 4,396,010 to Arkans, discloses a time-based sequential compression device for simultaneously inflating multiple limb sleeves. Time-based sequential compression devices are also publicly available from The Kendall Company, of Massachusetts. For example, FIG. 1 illustrates an experimentally derived graph of an inflation cycle for a Model 5325 sequential compression device, manufactured by The Kendall Company. It is believed, however, that none of these sequential compression devices and methods provide for optimum blood flow velocity and volumetric flow rate in recumbent patients.
Thus, notwithstanding these attempts to develop compression devices for preventing deep vein thrombosis and pulmonary embolism, there continues to be a need for a gradient sequential compression system which provides a high blood flow velocity and a highly therapeutic prophylactic modality to limbs of a recumbent user.
It is therefore an object of the present invention to provide a system and method for reducing the occurrence of deep vein thrombosis (DVT) and pulmonary embolism in recumbent users.
It is also an object of the present invention to provide a system and method for achieving a high venous blood flow rate in a limb of a user.
It is another object of the present invention to provide a system and method of sequentially establishing a gradient of compressive forces, which is pressure-based.
It is a further object of the present invention to provide a system and method of regulating a gradient of compressive forces, using real-time feedback.
It is still a further object of the present invention to provide a system and method of providing a prophylactic modality to limbs of a user in an alternating sequence.
It is another object of the present invention to provide a system and method for determining the selected mode of operation used for achieving a high venous blood flow rate in a body portion of a user based on the type of compression sleeve or the particular body portion to be treated.
It is still a further object of the present invention to provide a universal connecting device and method that identifies a mode of operation associated with a connector mated thereto and provides a signal indicative of the mode of operation to the system such that the system may be automatically configured to the selected mode of operation.
These and other objects, features and advantages of the present invention are provided by a compression system and method which provides cyclical squeezing and relaxing action to one or more limbs of a user. This occurs by sequentially establishing a decreasing gradient of compressive forces along the limbs in a proximal direction. In particular, the compression system includes one or more sleeves (e.g., calf, thigh, calf and thigh, arm, forearm, torso, etc.) which can be wrapped around and releasably secured to a limb(s) of a user. The sleeves have one or more inflatable chambers therein for retaining pressurized air upon inflation and for applying a compressive force to a limb. The compression system also includes a system controller for controlling transfers of pressurized air from an external or internal source to the inflatable chambers of the sleeves during respective inflation cycles, and for venting the pressurized air during respective deflation cycles. Transfers of air from the system controller to the sleeves are preferably provided by pneumatic connecting means which can include first and second conduit means. First and second conduit means preferably include a plurality of separate conduits or conduit ribbon.
According to one embodiment of the present invention, the system controller includes control means and first and second pluralities of feeder valves, responsive to control means, for enabling and disabling transfers of air from the source to respective ones of the inflatable chambers. Control means is provided for controlling the sequence by which the feeder valves are directionally opened and closed so that during an inflation cycle a gradient of compressive forces can be sequentially established and maintained along a limb of a user for a predetermined time interval. In particular, according to a first embodiment, control means is provided for opening only one of the feeder valves to the source of pressurized air at a time, so that each of the inflatable chambers is independently inflated and regulated (e.g., measured and adjusted). Control means preferably includes a pressure transducer and means coupled thereto for sampling the pressures in each of the inflatable chambers and adjusting the pressures based on the samples so that the chambers are maintained at predetermined pressures, even if the limb sleeves are relatively loosely or tightly wrapped or the position of the limb is adjusted during treatment.
According to an aspect of the first embodiment of the present invention, the system controller includes first and second intermediate valves, connected between the source and the respective first and second pluralities of feeder valves. The intermediate valves, which are responsive to control means as well, enable transfer of air from the source to the first and second pluralities of feeder valves during respective first and second inflation cycles and vent air from the first and second pluralities of feeder valves during respective deflation cycles. In particular, the feeder valves and intermediate valves are directionally opened and closed to facilitate inflation, measurement and adjustment of the pressures in the limb sleeves.
The system controller also preferably includes means for sensing whether pneumatic connecting means is attached thereto. Sensing means may include an infrared, Hall effect or reflective sensor(s), for example. Control means also includes means, responsive to the sensing means, for automatically adjusting from a default two-limb mode of operation to a one-limb mode by preventing the occurrence of either the first or second inflation cycles if the respective first or second conduit means is disconnected from the system controller. The first and second inflation cycles are preferably 180xc2x0 out of phase so that only one limb sleeve is being inflated at a time.
According to another aspect of the present invention, the sensor also determines the selected mode of operation to be used by the controller. As stated previously, the current invention utilizes different compression sleeves. These compression sleeves contain different numbers of inflation chambers and are formed differently to conform to and adequately compress selected portions of the body (i.e., calf, thigh, calf and thigh, arm, forearm, torso, ect.). Further, the system utilizes different pressure cycles for providing treatment to different body portions. The controller of the present invention determines the proper mode of operation for the system by using a sensor. This sensor senses an indication from an indicator connected to the compression sleeve being used by the system. This indicator designates the mode of operation associated with the sleeve. In this embodiment, the sensor provides a signal to the controller that identifies the selected mode of operation indicated by the sleeve. The controller configures the system in accordance with this signal to operate in the selected mode of operation. This, in turn, allows for the automatic configuration of the controller for a selected treatment without the need for user input.
The system controller also includes means for detecting low and high pressure fault conditions which can be caused by disconnected or occluded conduits, and sleeves that are wrapped too loosely or too tightly about a limb.
According to yet another aspect of the invention, compressive forces are applied to a limb of a user by sequentially compressing a distal portion and then a relatively proximal portion of the limb to provide respective first and second radially inwardly directed compressive forces thereto. The first compressive force is maintained above the second compressive force so that a decreasing pressure gradient is established in a proximal direction along the limb for a preselected time interval. The force is preferably maintained by measuring the compressive forces and adjusting (i.e., increasing or decreasing) the compressive forces to maintain predetermined forces.
More particularly, the invention includes a method of applying compressive forces to a limb of a user using a multi-chambered inflatable limb sleeve surrounding the limb. The method includes the steps of pressurizing a first chamber of the limb sleeve to a first predetermined chamber pressure and then pressurizing a second chamber, disposed proximally relative to the first chamber, to a second preselected chamber pressure, after the first chamber reaches a first threshold pressure. The first threshold pressure may be less than or equal to the first predetermined pressure.
Preferably, the second chamber pressurizing step occurs after a pressure in the first chamber has been established at the first predetermined pressure for at least a first time interval. A step is also performed to regulate the pressures in the first and second chambers at their respective predetermined pressures so that a constant pressure gradient is established therebetween. The regulating step may include the steps of measuring a pressure in the first chamber while preventing depressurization of the second chamber and vice versa. Additionally, the regulating step may include the steps of measuring a pressure in the first chamber after it has been inflated to the first threshold pressure and then re-measuring a pressure in the first chamber, after the second chamber has been inflated to the second threshold pressure.
The pressures in the chambers may also be adjusted by performing periodic reinflating steps (and also deflating steps). Similar steps may also be performed to inflate third and fourth, etc. chambers of the limb sleeve, in sequence, so that a monotonically decreasing pressure gradient is established and maintained in a proximal direction between the chambers of a sleeve(s).
A periodic adjusting step may also be performed to adjust the pressures in the chambers during an inflation cycle, by sampling (once or repeatedly) a pressure in a respective chamber to obtain a pressure sample and then adjusting the pressure by inflating or deflating the respective chamber, based on the value of the sample. Pressure samples from a respective chamber during an inflation cycle can also be averaged to determine whether a critical overpressure condition occurred during a prior inflation cycle and/or occurred multiple consecutive times during prior inflation cycles. If a critical overpressure condition has occurred, subsequent inflation cycles can be disabled to maintain the respective sleeve(s) in a continuously deflated state until the system is reset or the critical condition is corrected. Thus, instantaneous pressure spikes can be compensated to prevent the occurrence of shutdown when a single or relatively few aberrant pressure samples have been measured.
According to a second embodiment of the present invention, each of the feeder valves described with respect to the first embodiment are replaced by a pair of filling and monitoring valves. The filling valves are preferably normally-closed valves and the monitoring valves are preferably normally-open valves. Here, the filling valves have an open state for enabling one-at-a-time transfer of pressured air from a source to the inflatable chambers of the first and second limb sleeves, in response to application of an energizing signal (e.g., logic 1), and a normally-closed blocking state which disconnects a respective chamber from the air source. In contrast, the monitoring valves have a normally-open state for enabling transfer of pressurized air from a respective inflatable chamber to an output thereof. These outputs are preferably pneumatically coupled through a corresponding three-way normally-open intermediate valve to a vent xe2x80x9cVxe2x80x9d or a pressure transducer in response to appropriate control signals. The monitoring valves also have a closed state (which can be achieved by application of an energizing signal (e.g., logic 1)) to prevent the escape of pressured air from a respective chamber when other chambers are being inflated or when the pressures in other chambers are being independently measured.
Control means, which is operatively connected to the filling, monitoring and intermediate valves, is provided for inflating a first inflatable chamber of the first limb sleeve by disposing the corresponding filling valve in an open state and the other filling valves in their respective normally-closed states. During inflation of the first inflatable chamber, the corresponding first monitoring valve is also disposed in a normally-open state so that the pressure in the first inflatable chamber can be measured in real time as it is being inflated and thereafter when the first inflatable chamber is fully inflated and the corresponding filling valve has been closed. Thus, in contrast to the first embodiment, the pressure in a chamber can be continuously measured as the chamber is being inflated to its respective predetermined pressure. This provides real-time feedback of the chamber pressure. Preferably, this real-time feedback is used by the control means to adjust the inflation time of the respective chamber during the current or subsequent inflation cycle(s). The amount of time needed to measure the pressure in a chamber after the respective filling valve closes can also be reduced because the pneumatic connecting lines between the respective monitoring valve and the pressure transducer will already be at least partially pressurized at the respective chamber pressure when the measurement operation commences.